1. Field of the Invention
The present invention relates to a switch driving device and a switch driving method for driving a switching element in a power supply device such as a DC-DC converter, for example.
2. Description of the Related Art
As power supply devices such as DC-DC converters, for example, switching power supply devices in which a switching element (semiconductor switch) such as a metal oxide semiconductor field effect transistor (MOSFET) or an insulated gate bipolar transistor (IGBT) is driven by a switch driving device (drive circuit) so as to convert power have been widely used.
In such a switching power supply device, the problem of a self-turn-on phenomenon in which a switching element in an OFF state is mistakenly turned ON may arise, for example, when the switching element is driven at high speed. In this self-turn-on phenomenon, a drain-source voltage in an OFF state sharply rises along with the high-speed driving of the switching element, for example. Charge is thus injected into gate-source capacitance (i.e., the gate-source capacitance is charged) via drain-gate feedback capacitance, thereby increasing a gate voltage to a threshold voltage or higher and thus turning the switching element ON. The occurrence of the self-turn-on phenomenon results in not only deteriorated power conversion efficiency but also, for example, the damage or firing of the switching element in some cases.
A known technique to prevent such a self-turn-on phenomenon is applying a negative voltage to a gate of a switching element in an OFF state so as to bias a gate voltage toward the negative side (see Japanese Patent No. 4945218 or Japanese Patent No. 4916964, for example). Biasing the gate voltage toward the negative side allows the gate voltage to be kept below a threshold voltage even when the amount of charge injected via feedback capacitance is large. Thus, the self-turn-on phenomenon can be effectively prevented from occurring.